The conformation of the non-collagenous (NC1) domain of the α3 chain of the basement membrane collagen IV [α3(IV)NC1] depends in part on phosphorylation. Goodpasture Antigen Binding Protein (GPBP) (WO 00/50607; WO 02/061430) is a novel non-conventional protein kinase that catalyzes the conformational isomerization of the α3(IV)NC1 domain during its supramolecular assembly, resulting in the production and stabilization of multiple α3(IV)NC1 conformers in basement membranes. Elevated levels of GPBP have been associated with the production of non-tolerized α3(IV)NC1 conformers, which conduct the autoimmune response mediating Goodpasture (“GP”) disease. In GP patients, autoantibodies against the non-collagenous C-terminal domain (NC1) of the type IV collagen α3 chain (“Goodpasture antigen” or “GP antigen”) cause a rapidly progressive glomerulonephritis and often lung hemorrhage, the two cardinal clinical manifestations of the GP syndrome.
The identification of GPBP provided methods for identification of compounds for the treatment of autoimmune disorders, cancer, protein misfolding-mediated disorders and aberrant apoptosis, and also provided potential therapeutics for these disorders. Thus, the identification of novel GPBP isoforms would be advantageous in at least these fields.